Schneider Electric Modicon 990 Series Modules: 990NAD21110 Connection Cable —

Technical Dossier

Product Details And Specifications

Schneider Electric Modicon 990 Series: Comprehensive Module Range and Technical Overview

The Schneider Electric Modicon 990 series represents one of the most widely deployed distributed I/O and communication infrastructure families in global heavy industry. Installed across petrochemical complexes, nuclear power facilities, offshore platforms, and continuous-process refineries, the 990 series serves as the physical interconnect and network backbone layer for Modicon Quantum and Premium PLC architectures. Its prevalence in safety-critical environments — where system uptime is measured in years, not hours — has made the 990 series a long-term fixture in industrial spare parts inventories worldwide. The series encompasses connection cables, network adapters, communication modules, and bus extenders, all engineered to operate within the deterministic timing requirements of Modbus Plus, Ethernet, and proprietary Modicon backplane protocols.

The Evolution of Modicon 990 Series Architecture

The 990 series originated as the physical-layer complement to the Modicon Quantum platform, introduced in the early 1990s as Schneider Electric (then Modicon/AEG) standardized its distributed I/O strategy around the S908 remote I/O bus. Early variants such as the 990NAA26320 and 990NAD21100 established the coaxial and twisted-pair cabling standards that would define field wiring practice for the next two decades.

As industrial networking evolved from proprietary S908 and Modbus Plus topologies toward Ethernet-based architectures (Modbus TCP/IP, EtherNet/IP), the 990 series expanded to include fiber-optic repeaters, TCP/IP bridge modules, and high-density I/O drop adapters. Compatibility between generations is constrained by physical connector type (BNC, RJ45, DB9, proprietary Modicon headers) and protocol layer — S908 drop adapters are not interchangeable with Modbus Plus network adapters without topology redesign.

By the 2010s, Schneider Electric formally transitioned new installations toward the Modicon M580 and EcoStruxure Automation Expert platforms. The 990 series entered a managed end-of-life phase, with most catalog numbers moving to last-time-buy or obsolete status. This transition has elevated the strategic importance of aftermarket sourcing for facilities that cannot justify full system migration.

Modicon 990 Series Full Catalog & Functionalities (SKU List)

Connection Cables & Physical Layer

• 990NAD21100: S908 remote I/O drop cable, 1 m, straight connector, standard drop adapter interface
• 990NAD21110: S908 remote I/O connection cable, extended length variant, compatible with Quantum drop adapters
• 990NAD21120: S908 coaxial trunk cable segment, 2 m, BNC termination, for main I/O bus trunk extension
• 990NAD21130: S908 coaxial drop cable, 3 m, right-angle BNC, for panel-mount drop adapter installations
• 990NAA26320: Modbus Plus network cable, 1 m, DB9 male-to-male, for node-to-node daisy-chain wiring
• 990NAA26350: Modbus Plus network cable, 3 m, shielded twisted pair, for extended node spacing

Network Adapters & Communication Modules

• 990NAD21200: S908 remote I/O drop adapter, single-slot, for Quantum I/O rack integration
• 990NAD21210: S908 remote I/O drop adapter, dual-port, supports redundant trunk wiring
• 990NSD111100: Modbus Plus to S908 bridge adapter, enables legacy S908 drops on Modbus Plus networks
• 990XCP95400: Modbus Plus PCMCIA network adapter, for programming terminal and SCADA host connection
• 990NAE21100: Ethernet TCP/IP network adapter, 10BASE-T, for Quantum CPU Ethernet port extension
• 990NAE21105: Ethernet TCP/IP adapter, 100BASE-TX, RJ45, for high-speed Modbus TCP/IP network drops

Bus Extenders & Repeaters

• 990NAD21300: S908 coaxial bus repeater, extends trunk segment beyond 300 m standard limit
• 990NAD21310: S908 fiber-optic repeater, single-mode, for electrically noisy or long-distance trunk runs
• 990NAD21320: S908 fiber-optic repeater, multi-mode, 62.5/125 µm fiber, for inter-building I/O bus extension

Power & Termination Accessories

• 990NAD21400: S908 bus terminator plug, BNC, required at each physical end of the coaxial trunk segment
• 990XCP95100: Modbus Plus network terminator, 150 Ω, DB9 form factor, for network segment end-of-line termination

Sourcing Hard-to-Find & Obsolete Modicon 990 Series Parts

The majority of the Modicon 990 series catalog has been discontinued by Schneider Electric. Standard distribution channels no longer carry active stock for most 990NAD and 990NAA part numbers. For facilities operating Quantum-based DCS or PLC systems — particularly in refinery, chemical, and power generation environments where control system replacement cycles span 15–25 years — maintaining a reliable supply of 990 series components is a direct operational requirement.

DriveKNMS maintains a dedicated inventory of new-surplus, refurbished, and tested 990 series modules sourced from decommissioned systems, authorized liquidations, and long-term storage. Each unit undergoes functional verification before dispatch. For critical infrastructure applications, DriveKNMS can provide multi-year supply agreements to support planned maintenance schedules and emergency breakdown response.

Quality Control for the Modicon 990 Series Range

The 990 series presents specific testing challenges due to its role as a physical and protocol-layer interface component. Connection cables are tested for continuity, impedance matching (93 Ω nominal for S908 coaxial), and connector integrity under repeated mating cycles. Network adapters and bridge modules undergo protocol-level verification using Modicon Quantum test racks, confirming correct S908 frame transmission, Modbus Plus token-passing participation, and Ethernet TCP/IP register read/write response.

Fiber-optic repeater units are tested for optical power budget (transmit power, receive sensitivity, and link margin) using calibrated optical power meters. All refurbished units are cleaned, re-labeled with DriveKNMS traceability codes, and shipped with test reports on request. Units that fail any functional parameter are quarantined and not offered for sale.